1. Field of the Invention
This invention relates to a method of adhering rubber articles, and more particularly to an adhesion method for rubber articles which is suitable for the adhesion of vulcanized rubber articles at a low temperature of not higher than 100.degree. C, preferably not higher than 50.degree. C., such as retreading adhesion of tires, repair the broken-off portion in tires, conveyor belts and the like, and forming numerous conveyor belts and so on.
2. Related Art Statement
At the present, the retreading adhesion of tires is carried out by a precure system. That is, a rubber cement is applied to a surface of each of a base tire and a precure tread to be adhered, and a cushion rubber is sandwiched between these surfaces covered with the rubber cement, and then these members are bonded by vulcanization at a high temperature of not lower than 120.degree. C., usually about 150.degree. C. However, such a system has the following problems:
(1) It is necessary to conduct the vulcanization in an autoclave at a high temperature under a high pressure, so that it is required to use large-size equipment; PA1 (2) Since the vulcanized base tire and tread are again exposed to a high temperature exceeding 120.degree. C., the properties and performances of these members may be degraded. PA1 (1) Since the thickness of the adhesion rubber layer is too small, it is difficult to obtain a large peeling strength; PA1 (2) When using an adherend having many large and small uneven areas such as a retreading base tire or the like, it is difficult to uniformly apply the adhesive solution, so that the true adhered portion is not a plane form but is apt to be rendered into dot-like form. PA1 (I) applying a rubber cement composition, which comprises 100 parts by weight of natural rubber (NR) or isoprene rubber (IR), 1-5 parts by weight of sulfur or an organic sulfur compound having two or more sulfur atoms, 1-15 parts by weight of a ultrarapid accelerator, 2-15 parts by weight of an organic amine having a base dissociation constant (pK.sub.b) of not more than 5, 30-70 parts by weight of carbon black and proper amounts of zinc white and organic solvent, to surfaces of the vulcanized rubbers to be adhered and drying it; PA1 (II) sandwiching an unvulcanized rubber sheet of a cushion rubber composition, which comprises 100 parts by weight of natural rubber (NR) or isoprene rubber (IR), 1-5 parts by weight of sulfur, 1-7 parts by weight of an organic amine having a base dissociation constant (pK.sub.b) of not more than 5, 30-70 parts by weight of carbon black and a proper amount of zinc white, between the applied surfaces of the vulcanized rubbers and vulcanizing them at a temperature of 0.degree.-100.degree. C. under pressure.
Therefore, it is strongly demanded to develop a method of adhesion through vulcanization at a temperature of not higher than 100.degree. C., preferably not higher than 50.degree. C.
On the other hand, a method of adhering vulcanized rubber articles through vulcanization at a temperature of not higher than 100.degree. C. is disclosed in Japanese Patent Application Publication No. 49-24972 and the like. In this method, a rubber composition obtained by compounding particular amounts of sulfur or an organic sulfur compound and aliphatic amine with an unvulcanized unsaturated rubber having a relatively small content of unsaturated double bond such as EPT, butyl rubber or the like is dissolved in an organic solvent, which is applied to surfaces of vulcanized rubber articles to be adhered. Then, the applied surfaces after the drying are stuck to each other and left to stand at a temperature of, for example, 40.degree. C. However, this method has also the following problems:
Furthermore, a repair material for rubber tire called by the trade name of Tip-Top is commercialized by Stahl Gruber GMBH & Co. in West Germany. However, this material has a low peeling strength at a high temperature (100.degree. C.) and a low peeling strength after the aging and is unsuitable for retreading adhesion of tires.